Dental cements of the so-called "glass-ionomer" variety are formed by reacting a fluoroaluminosilicate glass powder ("glass") and a poly(carboxylic acid) ("polyacid") in the presence of water. The mixture undergoes a brief working period, during which the reactants are converted from a creamy paste to a relatively firm, carvable solid. The working period is followed by a brief setting period, during which the carvable solid becomes sufficiently strong to function as a dental cement. The cured cement provides an ion-leachable source of fluoride with beneficial cariostatic properties. Work time, set time and mix viscosity of the cement are each important to the user, and tend to govern market acceptability of the cement. Most dentists prefer longer work times and faster set times. Unfortunately, when set times are accelerated by the usual methods, work times are also reduced.
Virtually all commercially available glass ionomer cements include a chelating agent (usually tartaric acid) that adjusts the work time and set time of the cement. Such chelating agents are described in U.S. Pat. Nos. 4,209,434, 4,089,830, 4,317,681 and 4,374,936, and in Prosser et al., "NMR Spectroscopy of Dental Materials. II. The role of Tartaric Acid in Glass-Ionomer Cements", J. Bio. Mat. Res., 16, 431-445 (1982).
Work time and set time can also be adjusted by controlling the particle size and surface area of the glass; by treating the glass with an acid, thoroughly washing the treated glass to leave substantially no soluble calcium salts on the surface of the glass particles, and drying the washed particles (U.S. Pat. No. 4,376,835); by controlling the molecular weight and carboxyl equivalent weight of the polyacid; or by controlling the ratio of glass to polyacid.